Manufacture of smokeless powder



Oct. 20, 1953 w PIPER 2,655,694-

MANUFACTURE OF SMOKELESS POWDER Filed July 28, 1945 5HE T 0F COLLO/DED5MOKELE$5 POWDER COMPOSITION STRIPS cur FROM ABOVE :E'ilj: 4

VACUUM EXTRUS/ON PRESS ROLL FORMED FOR EXTRUDING ROLL FROM ABOVE OF Fla3 STRIP SOL/D CYL/NDR/CAL. COPE OF .SIVOKELESS POWDER COMPOSITIONSIMILAR TO COMPOSITION OF THE ABOVE.

SHEET 4 gvwc/wfo'v Willi-min E. Piper Patented Oct. 20, 1953 res ear mOFFICE MANUFACTURE OF SMOKELESS POWDER Application July 28, 1945, SerialNo. 607,666

9 Claims.

This invention relates to a method of preparing smokeless powder grains,and more particularly to an improved method of extruding rolled sheetpowder to produce a thick-web, large powder grain with improvedcharacteristics.

Smokeless powder to be used as the propellent charge in jet-actuateddevices, such as rockets, jet-assisted take-off devices, and the like,is made into the form of large, thick-web grains. An important reasonfor this is to obtain a small ratio of burning surface to quantity ofmaterial, so that the pressure resulting from burning will not bedeveloped too quickly after ignition. In order to prevent erraticchanges in pressure during the burning, it is necessary to avoidfissures in the finished powder grain and/or stresses and other causeswhich will result in fissuring during the burning of the grain. In orderto insure uniform ballistics, each such large grain of powder iscarefully inspected by X-rays and the like to detect fissures within thegrain. Fissured grains are rejected and reworked.

In general, there are two methods of preparing thick-web, large grainsof smokeless powder. In one method, commonly referred to as the solventmethod, the powder constituents are colloided with the aid of volatilesolvents, pressed into uniform blocks of colloided powder, extruded orotherwise molded to the right dimensions, and then treated for theremoval of the volatile solvent. This method has a number ofdisadvantages, particularly in making large grains, arising from theexpense and dificulty of removing and recovering the volatile solvents.In the other method, commonly referred to as the solventless method, theingredients are uniformly mixed and made into a wet paste, the water isremoved by drying, the resulting dry paste is colloided by rolling, thecolloided mass is rolled into sheets, the sheet material is made into acarpet roll, the carpet roll is extruded by means of a suitable pressinto the desired grain shape and then cut into grains of the desiredlength.

Heretofore, in the manufacture of large grains of smokeless powder foruse in jet-propelled devices, by the solventless method, a very highpercentage of rejections has resulted on account of fissures in thepowder grain. The percentage of grains or sticks having fissures asdetected by X-rays, in general, has varied from about 6.9 to 10.2% ofall sticks examined; in some instances, fissure frequencies of over 20%have been recorded over relatively short periods of time.

Now, in accordance with the present invention, a method has beendiscovered for producing an extruded plastic mass, having a relativelylarge cross-sectional area with a marked reduction in the number offissures in the extruded product, from a roll made from a sheet of theplastic mass.

Generally described, the improved method in accordance with thisinvention comprises rolling a sheet of the colloided material onto asolid core of similar colloided material, thus forming a carpet rollwith a solid core center, placing the carpet roll in an extrusion pressprovided with a suitable die, removing the air from the press chamber byevacuation and maintaining the chamber under vacuum, and then extrudingthe material by the application of pressure thereto.

Described more specifically, the method comprises preparing a rolledsheet of a colloided smokeless powder composition, cutting the sheetinto strips of any desired and convenient width, rolling the strips intothe form of carpet rolls onto solid cores of a similar colloidedsmokeless powder composition, placing one or more of said rolls into thepress chamber of an extrusion press provided with a reciprocatingpiston, evacuating the press chamber, and then extruding the powderthrough a suitable die to give an extruded product with a largecross-sectional area and of any desired cross-sectional configuration.

The method is illustrated, partly diagrammatically, in the accompanyingdrawings, wherein Fig. 1 represents a plan view of a sheet of colloidedsmokeless powder composition; Fig. 2, plan views of five strips cut fromthe sheet illustrated in Fig. 1; Fig. 3, a carpet roll formed by rollingstrips of the kind illustrated in Fig. 2 onto a solid cylindrical coreof a colloided smokeless powder composition similar to the compositionof the sheet of Fig. 1; Fig. 4, an extrusion press of the type indicatedabove; and Fig. 5, a powder grain of cruciform cross-section resultingfrom the operation of the extrusion press of Fig. 4 upon the roll ofFig. 3.

Having now indicated in a general way the nature and purpose of theinvention, there follows a more detailed description of a preferred embodiment thereof in the following example:

Fifty-one parts of nitrocellulose (13.25% nitrogen) of lint base, about43 parts of nitroglycerin, about 3 parts of diethyl phthalate, about 1part of ethyl centralite, all parts by weight, and a small amount ofcarbon black and candelilla wax, were made into a wet paste by knownmethods. The wet paste was air-dried to about 12-14% moisture contentand then blended and uniformly mixed with about one part by weight (samebasis as for above constituents) of finely- 3 subdivided potassiumsulfate to give a final dry paste.

The dry paste, in 6-pound charges, was rolled on one or moredifferential roll assemblies at a temperature of about 210 F. untilhomogeneous, colloided sheets were obtained. The colloided sheets werestripped from the rolls, cooled, and then several-such sheets, togetherWith rolled sheets of reworked material, werestacked together and madeinto a single sheet by passing through an even speed roll assembly.

The sheet from the even speed.rolls..was -cut into strips about incheswide and"severalfeet long. The strips were thenwrolledv onto solid rods(about 1 /2 inches in idiameter) :of sazsimilar colloided powdercomposition .totiormsso-called carpet rolls. The carpet rolls..,thus.formed were about 5 inches long and aboutIO inches indiameter and hadsolid longitudinal centersicores.

Two of the thus prepared carpet rolls were placed end .to end inthepress .chamber .of...an ,oildraulic horizontal extrusionpress..The,.press chamber was evacuated andithe chargcwonsisting of about 50pounds, was.extr.u'ded. into. asingle continuous long. grain of.cruciformscrosssec- .tion which was ,cut intojfivesticksor grains,.each

.fmeasuring about T217 1 inches Jdiametr-ically -across the arms .andabout $34 inches longitudinally. The. arms .of I the cruciform wereabout 3.110 inch thick, .the :controlling webithitzkness of..this..ty.pe .gl'alin.

" The-,grains .were anneaIe'dLby being. exposedato air .at? 140.1'Fffor-.45 hours. IiThey werathengiven an inspectionfondimensional.to1erances:and.surface characteristics, followed 'Izby-an ;X-.ray exanimation for internalifiaws; particiilarlylissures.

The results/of thelinspectionofsticks i grains) .of. powderrma'dein-accordance .with this; example. are. given in.tabular;for1rLbelow,.tQgether with ..comparable .dataforsticksofithesameitypeoand 40 -..,composition preparedinan identicalmanner ex-.cept .for .omissioneof.the.solid.core,:,provided.=or

.the .carpet ,rolls. L'Thetabulated ldataareier to inspections .made von.several .thousandlsing le grains ..(sticks) -in .the course ..ofapproximately one .weeks plant.operation1bylhighlysskilledioperatorsin-eachcase.

The:foregoingresultsiiemonstrate conclusively the improvement-insulting.fromrthezmethod accordanceavith-- this invention wherein theecar- ..pet.roll' was? provided with: a-,,-solid .center'. instead of the-usualhollow center z-which-always results from simply rollinga sheet (strip)zofwthe :fairly :stiff colloided, powdeniormulatiom. although ;the

sheet. is warmed to soften. it .prior.,.to.;rol1ing.

The improved powder grains produced in accordance with this inventionexhibited fissuring to a markedly smaller extent than sticks producedwithout the solid center core. Although the improved results wereassociated with what might be termed the central longitudinal section ofthe powder sticks, it Was evident that -fissuring.-.occurre.dtoeazsmallera-extent even in the arm's-sections of the'cruciform'stick,i. e., in sections which did not contain any of the powder zmaterial ofthe solid center core.

-Erom..examination of successive cross sections of the extrude'd'grainsfrom rolled sheet powder awithoutrsolidt-corezcenters, it would appearthat :thescentemholenwas responsible for most of the fissuring. Further,it would appear that a major -portion of,-,this,fissuring cause waseliminated in the first portion extruded. Thus, the followingresults.=-show that the largest percentage of bad sticks due to fissuresis to be found in the first ..portion of the extruded, powder.

TABLE "2 .Dz'stributz'on :0) fissures in "total of :104 :fissured sticksPercent Stl'ckNo. 35: 2:35

sticks i 1 (first part of extrusion) .L

Thus-sover two-fifths of the ""fissu-redsticks are inthe'first-z'one-fifthof the extruded' pow'der.

'From =the comparative results obtained with "and without 'a sol-idcenter-core; it appears that 1 the causeof-thefissuresyavhen a solidcenter core is not=-used,=is that some of the airin the-hollow center isnot removed even when the presschamzber *is 1 evacuated. Furthermore,-even vv-ith *substantial removal of the air from 'the hollow cen- 1ter,- 'this wou1d be expected to cause collapseof circumsciibed layersof the "sheet powder -=with "resultant buckling of *the 'layers'and-entrapment I of air :at -other places throughout the 'powder. "Thesephenomena would be eliminated by preventing the possibility'o'f"coll-apse'ofthematerial --upon =evacuation *such as by 'providing '-theroll :with a solidacenter core. 'Although this appears to be=a'reasonable'explanatiomfor*:the* improvement resulting fromapplication of this invention, it "is not intended that theinvention-shall 'be' l-imited to any-particular"theory of operation. Intheforegoing example the colloidedpowder (sheet was preparediwithout theaid ofvolatile solvents, such sas @alcoholp ether, acetone, and i the 1like,; .as well 5 as mixtures rthereof. .However, sexztrusions from;-:solvent-type, .ccolloided powder .:sheetcmay:.bez mafdezaccording :tothe methodzof this invention with s-similarximprovement. .The qpowder 1constituents: may.-,be-..co1loided tbysiknown -methods and :withthe21156.10f- V019r13118L0l311i0 :solvents, .thecolloidedimass @i-nade:intmsheets, -..the volatile solvent 1or.=solvents .removed Joy-knownimethods the sheetsmade into -a carpet.- roll pro- .-v-ided .with a,so1id..center..core, andsextruded.

The solid reenter -core'may .be .of any suitable dimensions, which..of.course, will; beJdetermined .by,.the dimensions, particularly.crossesectional, of. 'the graimto -be prepare'dby extrusion. Of course,vi.the -cross .section .will Lbe limited .to a uninimumbrosssectionwhich .willlbe dependentupon the particular physical characteristics ofthe sheet. Thus, a formulation which gives a very stiff sheet willrequire a larger core than one which can be bent and folded over easilyto form a roll with a small hollow center. The maximum diameter of thecore will be limited only by the maximum allowable core-type material inthe finished grain, on account of any possible differences in ballisticsand other characteristics. The solid rod to be used as the solid centercore was prepared from a roll of colloided sheet powder, similar to thatto be extruded, by extrusion under pressure using a circular die of theappropriate size. Solid rods free of fissures are selected for use.

This invention is of utility in the manufacture of thick-web, largegrains of smokeless powder adapted for use in jet-propelled devices. Asindicated hereinbefore, powder grains for such use are advantageouslyprepared by rolling a sheet of the colloided powder into the form of acarpet roll and then extruding it axially of the roll through a suitabledie, such as of a cruciform shape. Heretofore, such practice hasresulted in the preparation of a large number of rejects orunsatisfactory powder sticks on ac count of fissures present in thepowder stick. The proportion of such unsatisfactory sticks isadvantageously reduced when practicing the method of this invention.This increases materially the capacity of a given unit of plantfacilities, decreases the total number of inspections required for agiven net quantity of satisfactory sticks, decreases the hazardsinvolved in reworking unsatisfactory sticks, etc. All such advantagesare gained without any disadvantageous effects, such as alteration inballistic properties, and the like, contrary to what was expected and asindicated in earlier specifications for rocket powder grains. Thedemonstration of advantages without corresponding disadvantages issubstantiated by the alteration of earlier Government specification soas to specify now the use of a solid center core in extruding sheetpowder for thick-web, large grains of smokeless powder for rocket use.

Where in the specification and appended claims the term thick-web, largegrain is used, it is meant to designate a powder grain having a minimumburning web of about 0.25 inch and to have a length greater than the webthickness.

What I claim and desire to protect by Letters Patent is:

1. In the art of forming thick-web, large grain smokeless powder byextruding longitudinally a roll prepared from a sheet of colloidedsmokeless powder, the improvement which comprises preparing said roll byrolling a sheet of said powder onto a solid core of colloided smokelesspowder.

In the art of forming thick-web, large grain smokeless powder byextruding longitudinally a roll prepared from a sheet of colloidedsmokeless powder, the improvement which comprises preparing said roll byrolling a sheet of colloided smokeless powder about a solid core ofcolloided smokeless powder.

3. The method of forming thick-web, large grain smokeless powder from acolloided sheet of said powder which comprises forming the sheet ofcolloided powder into a roll provided with a solid core of colloidedsmokeless powder, and extruding said powder axially into a thickweb,large grain.

4. The method of forming thick-web, large grain smokeless powder from acolloided sheet of said powder which comprises rolling the sheet ofcolloided powder into a carpet roll provided with a solid core ofcolloided smokeless powder, and extruding said powder axially into athickweb, large grain.

5. The method of forming thick-web, large grain smokeless powder from acolloided sheet of said powder which comprises rolling the sheet ofcolloided powder about a solid core of colloided smokeless powder, andextruding said powder axially into a thick-web, large grain.

6. The method of forming thick-web, large grain smokeless powder from acolloided sheet of said powder which comprises forming the sheet ofcolloided powder into a roll provided with a solid core of colloidedsmokeless powder, and extruding said powder axially into a thickweb,large grain having a solid center core.

7. The method of forming thick-web, large grain smokeless powder from acolloided sheet of said powder which comprises rolling the sheet ofcolloided powder about a solid core of colloided smokeless powder, andextruding said powder axially into a thick-web, large grain having asolid center core.

8. The method of preparing a thick-web, large grain smokeless powderwhich comprises preparing a sheet of colloided smokeless powder, rollingthe sheet of powder about a solid core of colloided smokeless powder,and extruding said powder into a thick-web, large grain.

9. The method of preparing a thick-web, large grain smokeless powderwhich comprises preparing a sheet of colloided smokeless powder in theabsence of volatile solvents therefor, rolling the sheet of powder abouta solid core of colloided smokeless powder, and extruding said powderinto a thick-web, large grain.

WILLIAM E. PIPER.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 620,775 Hoifmann Mar. 7, 1899 1,477,094 Wilson Dec. 11, 19231,994,164 Bailey Mar. 12, 1935 2,165,827 Zuckert July 11, 1939 2,229,131Root Jan. 21, 1941

1. IN THE ART OF FORMING THICK-WEB, LARGE GRAIN SMOKELESS POWDER BYEXTRUDING LONGITUDINALLY A ROLL PREPARED FROM A SHEET OF COLLOIDEDSMOKELESS POWDER, THE IMPROVEMENT WHICH COMPRISES PREPARING SAID ROLL BYROLLING A SHEET OF SAID POWDER ONTO A SOLID CORE OF COLLOIDED SMOKELESSPOWDER.